Evidence for Non-Existence

There is an excellent blog here at http://rationesola.blogspot.com

In this blog entry http://rationesola.blogspot.com/2010/11/is-it-rational-to-believe-in.html the author makes a convoluted case for the improbability of Christian (and general) supernaturalism. I don't know if the author is male or female, so I'm taking a purely 50/50 (and possibly slightly politically correct) punt that she is a female. I will correct this if required should I obtain evidence of that necessity!

She makes the following point about the rationality of holding a belief in the Christian supernatural realm that is bread-and-butter agnosticism (and with which I fully agree):

Even if we granted, for the sake of argument, that the Christian supernatural realm might exist, the evidence, in this situation, is so bad that withholding belief in the existence of such a realm (or of any other) would be the only rational position available.

More importantly, like any good agnostic, she doesn't overstate the case:

It is important to note that this is not the same thing as saying that it is rational to believe that a supernatural realm does not exist. That position is not justified by the evidence: so far as that goes, it might well exist. 

And finally, but almost superfluously: 

But equally, just because we cannot confirm that a supernatural realm does not exist, doesn’t make it rational to believe that it does exist.

She is making the point that it is not rational to believe in something without evidence.

But then, in a footnote:

Another way of putting this is to speak in terms of probabilities. The absence of evidence for X doesn’t rule out the possibility that X could still exist. But it does make the existence of X highly improbable. So is it rationally acceptable to believe in something which, so far as the evidence goes, is highly improbable? 

Here is a glimpse of the the probabilities argument, elegantly graphed in Dawkins' The God Delusion, for positive atheism (for want of a better description) http://crtopherthinks.blogspot.com/2010/04/positive-and-negative.html

For if the absence of evidence for X makes X highly improbably and prompts the question "so is it rationally acceptable to believe in something which, so far as the evidence goes, is highly improbable?" then it equally suggests "is it rationally acceptable to NOT believe in something NOT existing, the existence of which, so far as the evidence goes, is highly improbable?"

In this quote the Solo Rationalist (yes yes I know....) appears to contradict her earlier point implying it would be less than rational to suggest the supernatural realm does not exist on the absence of evidence for its existence. In the probabilities argument, the absence of evidence makes it's existence highly improbable, and thus it's non-existence highly probable (since the probability coin can have only two sides). In this case it would seem quite rational to claim a belief in the non-existence of the supernatural, since to not believe in the non-existence of something that is highly improbable, is irrational!

I only make this point because many argue that agnosticism is the most rational position. And indeed on the face of it one must ask what constitutes evidence for the non-existence of something. Perhaps the probability concept will help me. I'm gonna think on it! BTW I don't mean to suggest that rationesola unknowingly contradicted herself. The footnote applied to an earlier part in the post than the part I initially quoted.